The perimeter of a rectangle is 240 feet and Its length is 12 less than it's width what are the dimensions of the rectangle?

Let the length be x-12 and the width be x:

2(length+width) = perimeter

2(x-12+x) = 240

2x-24+2x = 240

4x = 240+24

4x = 264

x = 66

Therefore: length = 54 feet and width = 66 feet